Adding leading zero to figure numbers

Question

I have a document that contains 31 figures. I'd like to configure the document such that figure numbers are printed with a leading zero, both in captions and in the list of figures (LOF). That is, I would like numbers to be written in the form

01, 02, ..., 09, 10, 11, ..., 30, 31.

I've seen this post about printing a counter with a leading zero, but I'm not sure how to (or if I should) apply that to modify the automatic numbering in the caption or LOF. I've generally been having success modifying the TOC, LOF, and LOT using tocloft, but as much as the package can do it doesn't seem to have any functionality regarding the figure or table numbers, and I don't imagine it would do anything to help with the actual captions.

---

I'm not sure what would be expected for a "MWE", but it would be sufficient for my purposes if someone could modify the below to have the desired leading zeros.

\documentclass[paper=letter, fontsize=11pt, twoside]{article}

\usepackage{graphicx}
\usepackage{tocloft}

\begin{document}


\listoffigures

\newpage 
\begin{figure}[!ht]
    Figure
    \caption{It's a figure}
\end{figure}    

\begin{figure}[!ht]
    Figure
    \caption{It's a figure}
\end{figure}    

\begin{figure}[!ht]
    Figure
    \caption{It's a figure}
\end{figure}    

\begin{figure}[!ht]
    Figure
    \caption{It's a figure}
\end{figure}    

\begin{figure}[!ht]
    Figure
    \caption{It's a figure}
\end{figure}    

\begin{figure}[!ht]
    Figure
    \caption{It's a figure}
\end{figure}    

\begin{figure}[!ht]
    Figure
    \caption{It's a figure}
\end{figure}    

\begin{figure}[!ht]
    Figure
    \caption{It's a figure}
\end{figure}    

\begin{figure}[!ht]
    Figure
    \caption{It's a figure}
\end{figure}    

\begin{figure}[!ht]
    Figure
    \caption{It's a figure}
\end{figure}    


    

    
    
\end{document}

Answer 1

Maybe an edit to your document will lower or increase the number of figures; or you want the same for tables.

I define an infrastructure that records in the aux file the maximum number of digits of the counter selected with \paddedcounter, so at the next run the padding can be done with respect to the number collected in the previous run. After a couple of runs the numbering will stabilize.

For simplicity, I make the (reasonable) assumption that you have less than 10000 figures.

\documentclass[11pt, twoside]{article}

\ExplSyntaxOn

\NewDocumentCommand{\paddedcounter}{m}
 {
  % protect against a not yet examined counter
  \AtBeginDocument
   {% we won't have more than 9999 figures
    \cs_if_exist:cF {maxdigits#1} { \cs_gset:cpn {maxdigits#1} {4} }
   }
  % at end document, store the number of digits of the last value
  \AtEndDocument
   {
    \iow_now:ce {@mainaux}
     {
      \token_to_str:N \maxdigits{#1}{\fp_eval:n{logb(\value{#1}+0.1)+1}}
     }
   }
  % pad
  \cs_gset:cpn {the#1} { \padded{#1} }
 }

\NewDocumentCommand{\maxdigits}{mm}
 {
  \cs_gset:cpn {maxdigits#1}{#2}
 }

\NewExpandableDocumentCommand{\padded}{m}
 {
  \prg_replicate:nn { \use:c { maxdigits#1 } - \tl_count:e { \arabic{#1} } } { 0 }
  \arabic{#1}
 }

\ExplSyntaxOff

\paddedcounter{figure}

\begin{document}

\listoffigures

\section{Test}

Test of reference: figure~\ref{test}

\begin{figure}[!ht]
    Figure
    \caption{It's a figure}\label{test}
\end{figure}    

\setcounter{figure}{9}

\begin{figure}[!ht]
    Figure
    \caption{It's a figure}
\end{figure}    

\end{document}

In the example I artificially increase the figure counter, so I pretend there are ten of them.

Commenting out the \setcounter{figure}{9} statement, the output will become

Answer 2

A solution which employs LaTeX's internal \two@digits macro: Just add the instructions

\makeatletter
\renewcommand\thefigure{\two@digits{\value{figure}}}
\makeatother

to the preamble.

Addendum: The \two@digits macro, which takes 1 argument, is defined as follows in the LaTeX kernel:

\def\two@digits#1{\ifnum#1<10 0\fi\number#1}

Answer 3

As per my comment:

\documentclass[paper=letter, fontsize=11pt, twoside]{article}

\usepackage{graphicx}
\usepackage{tocloft}

\renewcommand{\thefigure}{\ifnum\value{figure}<10
  0\arabic{figure}%
\else
  \arabic{figure}%
\fi}

\begin{document}


\listoffigures

\newpage 
\begin{figure}[!ht]
    Figure
    \caption{It's a figure}
\end{figure}    

\begin{figure}[!ht]
    Figure
    \caption{It's a figure}
\end{figure}    

\begin{figure}[!ht]
    Figure
    \caption{It's a figure}
\end{figure}    

\begin{figure}[!ht]
    Figure
    \caption{It's a figure}
\end{figure}    

\begin{figure}[!ht]
    Figure
    \caption{It's a figure}
\end{figure}    

\begin{figure}[!ht]
    Figure
    \caption{It's a figure}
\end{figure}    

\begin{figure}[!ht]
    Figure
    \caption{It's a figure}
\end{figure}    

\begin{figure}[!ht]
    Figure
    \caption{It's a figure}
\end{figure}    

\begin{figure}[!ht]
    Figure
    \caption{It's a figure}
\end{figure}    

\begin{figure}[!ht]
    Figure
    \caption{It's a figure}
\end{figure}    
    
\end{document}